Treffer: Evidence for a Mixture of Serial and Parallel Processing for Composite Morphed Faces

Several recent reports have identified that composite faces are likely processed with a mixture of serial and parallel architectures across trials. This type of processing is consistent with the theoretical idea that selective attention is employed in a more controlled fashion on some trials than other. In the present paper, we examine whether composite face processing shows evidence of a fixed cross over point in the response time distributions across different conditions. The existence of a fixed point would provide strong support for the mixture model explanation of composite face processing. We manipulated the proportions of serial and parallel processing by varying the horizontal distance between the top and bottom halves of a composite face in a four-item identification task. Across six observers, only two met the pre-requisite conditions for evaluating the fixed point property. Of these two, both showed evidence of a single mixed crossover point in line with the strong prediction of the mixture model.